Imaging drifting even though I’m guiding

Hey, I can help you with that. I have been using an EQ3-2 with terrible DEC backlash, a 360mm focal distance guiding scope, and a very weak camera for guiding. What I see is, polar alignment is sure a big deal when guiding on a mount with loads of backlash and a rather not sensible camera.

The best alterative would be adquiring a sensible camera. This alone would solve most of the backlash problem as having a sensible camera literally wont make the backlash happen (most of the times) in the first place. But taking that option away, with what you got, there are some things you can do to improve guiding overall:

1- When guiding, find the brightest star possible to guide with. Something i noted on my experience is that, whenever a almost transparent cloud passed by, my guiding would become really unstable and completely lost. Also, whenever I had a dim star as the guiding star, the program would think it was noise and catch on other white pixels and start guiding on noise. That would deliver me a low error, but obviously it was as if guiding was tuned off. If you only have dim stars in your field, tilt your scope until you can find one.

2- Increase the range the program will seek for the star. With a low sensibility camera, it is good to increase that number whenever you find a bright star. But make sure to not put that range between two stars, as the program might "jump" among them and make a complete mess. Just keep in mind to increase the camera contrast so you won't catch on noise as a guiding star.

3- As your main scope has 1500mm of focal distance, i usually use a tip i heard somewhere. It goes like this: you divide your main focal distance by 5 and this will be your guidescope ideal focal distance. In your case, I would use at least 300mm for proper guiding without overloading the weight capacity.

4- Make sure your mount doesn't have any loosen up screws. Specially the ones who attach it to the tripod or keep the polar alignment in place. Even the polar scope screws ust be tightened up, as any movement can worsen your guiding process.

5- Another thing that might work depending on your case is slightly unbalancing your mount RA or DEC to the opposite side of your backlash error. This way, the backlash MIGHT be balanced. For some mounts it works, for others (mostly), it helps a bit, and for some it worsens the problem. Keep in mind that the imbalance is minimum, think about it as leaving some momentum on the opposite side of the error.

6- There are some screws that will be responsible for keeping your mount's worm gear in place. I am no expert on the CGEM mount, but a quick research will teach you how to find them and fine tune them. On my personal case, finding the sweet spot beetween tighteness and looseness to release part of the backlash took me a whole month of try and error. It's a boring and irritating process. But it is so much worth, as you will get rid of a HUGE part of the backlash.

7- Unfortunately, mounts are not perfect. The more gears you have, the bigger it is, the less backlash you will have. But for EQ3s and EQ5s it's much more difficult to not have this problem. So, your guiding should not let the backlash happen at all, but sometimes, for any reason inside the gears, it might happen. So accept the fact that you might not get all pinpont frames, try to reduce your exposure time (specially if youre under light polluted skies), and remember that quality is better than quantity.

8- Last resource, if you try to adquire a sensible camera, like the asi 120 mini, and if you have tried every method above and you still have backlash and can't guide, it's time to take your mount to fix. I had friends who owned the CGEM mount and they'd have incessant problems with guiding on it, gigantic erros, even worse than my EQ3-2. So, keep in mind that you might need to open it yourself if you have the experience with gears and bearings and try to lubrificate it all over again, change whatever is needed, watch out for guides on how to fix it. But this is a last resource; i'm sure simple measures might help you to get 1'00 eror or even less. Ater trying all of the measures above, I could be able to get a 0'5 guiding error most of the times when guiding on a bight star.

This process is tiring, but I'm sure some of these tips can help you.

Clear skies,
Olga

Hey, I can help you with that. I have been using an EQ3-2 with terrible DEC backlash, a 360mm focal distance guiding scope, and a very weak camera for guiding. What I see is, polar alignment is sure a big deal when guiding on a mount with loads of backlash and a rather not sensible camera.

The best alterative would be adquiring a sensible camera. This alone would solve most of the backlash problem as having a sensible camera literally wont make the backlash happen (most of the times) in the first place. But taking that option away, with what you got, there are some things you can do to improve guiding overall:

1- When guiding, find the brightest star possible to guide with. Something i noted on my experience is that, whenever a almost transparent cloud passed by, my guiding would become really unstable and completely lost. Also, whenever I had a dim star as the guiding star, the program would think it was noise and catch on other white pixels and start guiding on noise. That would deliver me a low error, but obviously it was as if guiding was tuned off. If you only have dim stars in your field, tilt your scope until you can find one.

2- Increase the range the program will seek for the star. With a low sensibility camera, it is good to increase that number whenever you find a bright star. But make sure to not put that range between two stars, as the program might "jump" among them and make a complete mess. Just keep in mind to increase the camera contrast so you won't catch on noise as a guiding star.

3- As your main scope has 1500mm of focal distance, i usually use a tip i heard somewhere. It goes like this: you divide your main focal distance by 5 and this will be your guidescope ideal focal distance. In your case, I would use at least 300mm for proper guiding without overloading the weight capacity.

4- Make sure your mount doesn't have any loosen up screws. Specially the ones who attach it to the tripod or keep the polar alignment in place. Even the polar scope screws ust be tightened up, as any movement can worsen your guiding process.

5- Another thing that might work depending on your case is slightly unbalancing your mount RA or DEC to the opposite side of your backlash error. This way, the backlash MIGHT be balanced. For some mounts it works, for others (mostly), it helps a bit, and for some it worsens the problem. Keep in mind that the imbalance is minimum, think about it as leaving some momentum on the opposite side of the error.

6- There are some screws that will be responsible for keeping your mount's worm gear in place. I am no expert on the CGEM mount, but a quick research will teach you how to find them and fine tune them. On my personal case, finding the sweet spot beetween tighteness and looseness to release part of the backlash took me a whole month of try and error. It's a boring and irritating process. But it is so much worth, as you will get rid of a HUGE part of the backlash.

7- Unfortunately, mounts are not perfect. The more gears you have, the bigger it is, the less backlash you will have. But for EQ3s and EQ5s it's much more difficult to not have this problem. So, your guiding should not let the backlash happen at all, but sometimes, for any reason inside the gears, it might happen. So accept the fact that you might not get all pinpont frames, try to reduce your exposure time (specially if youre under light polluted skies), and remember that quality is better than quantity.

8- Last resource, if you try to adquire a sensible camera, like the asi 120 mini, and if you have tried every method above and you still have backlash and can't guide, it's time to take your mount to fix. I had friends who owned the CGEM mount and they'd have incessant problems with guiding on it, gigantic erros, even worse than my EQ3-2. So, keep in mind that you might need to open it yourself if you have the experience with gears and bearings and try to lubrificate it all over again, change whatever is needed, watch out for guides on how to fix it. But this is a last resource; i'm sure simple measures might help you to get 1'00 eror or even less. Ater trying all of the measures above, I could be able to get a 0'5 guiding error most of the times when guiding on a bight star.

This process is tiring, but I'm sure some of these tips can help you.

Clear skies,
Olga

Thanks Olga,

Already working on getting some new gear, I am actually imaging with my proper "guide camera" but you gotta work with what you got.

I do an east heavy balance to mitigate the RA backlash and i did maintenance to the RA. I'm unable to do the DEC yet its more complicated.

To avoid trails I do super short exposures 1 - 90 depends. What is weird though is i get less drift when im doing unguided. The only reason why i want the guiding to work is for dithering.

Great images by the way

Thanks

@Bob Lockwood 

im using sharp cap pro.

I never tried setting the aggressiveness to 0, it’s usually at the defaults for phd2.